Electric-wave-modulating system



1,633,016 June 1927' v. L. HARTLEY ELECTRIC WAVE MODULATING SYSTEM Filed July '7, 1925 v FL43' 6 4% 4/ f\ v /n vemar: Rap/2 VA. fiarf/ey Patented June 21. 1927.

UNITED STATES PATENT OFFICE.

RALPH-v. L. HARTLEY, or sou'rn' ORANGE, NEW JERsEy, ASSIGNOB r wns'rnmr unc'rmo COMPANY, INCORPORATED, or NEW YORK, N. .Y., A CORPORATION. or

NEW YORK.

.11am filed m '1,

ulating electric waves and in particular to systems for producing phase modulation.

The art of electric wave modulation, wherein the am litude of a carrier wave is varied in accor ance with theamplitudeof a modulating wave, usually a signal wave of some sort, is highlydeveloped and well understood. Likewise the fact that .modulation of carrier waves by shifting or varying the frequenc thereof in accordance with variations, usua ly amplitude variations of a modulating wave, is quite generally known. It is further known that, in both of the methods of modulation mentioned above, the resulting modulated waves are of a somewhat complex composition involving several components. One component is a waveof carrier frequency" unmodulated, a second is asideband of frequencies consisting of waves havingfrequencies represented by the sum of carrier and signal frequencies 'and a third component is a sideband of difference frequencies. However, in these two methods of modulation the relation which the unmodulated waves of carrier frequency bear to their respective side bands is different. If the side bands in both cases are identical as to phase, the unmodulated carrier wave in the frequency modulated system is in quadrature with the unmodulated carrier wave of the amplitude modulated system.

This invention comprehends. a third method of modulation wherein the phase of .the carrier wave is modified, and the resulting modulated wave components have phase relations the same as frequency modulated waves and amplitude relations the same as amplitude modulated waves.

An obiect of this invention is to modulate electric waves by varying their phase in, ac-' cordance with the variations of modulating waves.

Another object isto produce phase modulated waves and to suppress the unmodulated-component of carrierfrequency.

A further object is to produce phase mod ulated wavesand to generate other waves, which, by their combination with the phase ELEGTRIC-WAVE-MODULATING SYSTEM.

1925. serial No. 41,914.

modulated wave, enable reproduction of the modulating waves. 7 I

An additional object is to transmit signals by varying the phase of carrier waves in accordance with. signals and transmitting said modulatedfiwaves.

A further objectis'to produce undistorted phase .modulated waves.

A still further/object is. to maintain secrecy in the transmission of messages by carrler waves- A feature ofthe invention is an electromagneticsystem for producing phase modulated carrier waves which includes means for producing a rotating field of carrier frequency and means including a vibratory coil controlled by a signal source to cause modulation of the phase of currents induced therein by the rotating field.

Another feature is a means for generating a phase modulated wave including an unmodulated carrier component and in opposition thereto a wave of carrier frequency adapted to suppress the unmodulated comonent.'

A further feature is a means for 'gencrating an unmodulated carrier wave of such phase with respect to the sidebands of phase modulated waves that when combined with the phase modulated waves they may be detected to yield the modulating waves. The invention consists of an arrangement for generating carrier frequency waves and for shifting'the phase of these waves so as to cause modulatlon thereof, includes means for suppressing the. unmodulated carrier component of the modulated waves, and means for supplying an unmodulated component of carrier frequency in such phase relation to the sidebands that these latter may be combined in any well known detect ing device to yield the signals.v

The invention may. be practiced by generating a rotating field of carrier frequency and causing this field to traverse a coil which may be vibrated in accordance with modulating waves such as signal waves,

in opposition to that generated in the first coil, whereb this component may be suppressed. St1l1 another coil is provided and so arranged as to have induced in it a wave of carrier frequency of such phase relatively to the sideband components, that the induced wave and sidebands may be combined in any well known detector to yield the modulating wave.

In the drawings, a system for modulating the phase of a carrier wave in accordance with signals is illustrated.

The system includes a source of signals including a transformer 10 adapted to have its primary winding connected to a wire line, a mic-rop one speech transmitter or other source of signal waves. A signal translator 20, somewhat similar to a telephone receiver is connected to the transformer 10 and by a system of lovers 50 is adapted to produce an angular vibration of coils 30 and 31 of the modulator 32. The modulator is provided with output terminals 33 which may be connected to a wire line, an amplifier, a

ter. 7 a

The translating device 20 includes a polarized electromagnet 21 including windings 22 upon a permanently magnetized core 23. A diaphragm 24 is positioned in front of the pole faces of magnet 21 and is capable of vibration under the action of received waves.

At the center of the diaphragm 24 is attached a T-shaped arm 26 having rods 27 pivoted to its free ends. The rods are also pinioned to levers 28 rotatable about axes 29. The levers 28 are pivoted to rods 34 which in turn are pivoted to secondary levers 25. The latter are adapted to actuate rods 35 which are connected at their distant ends to lugs 36 mounted on the coils 30 and 31. The modulator 32 includes pairs of field coils 37 and 38 so positioned that their magnetic fields intersect each other and interlink with the coils 30, 31 and 40. The latter coil is stationary and is positioned coaxially with coils 30 and 31. Field coils 37 are connected in series to a source of carrier waves 41. Field coils 38 are likewise connected in series to a source of carrier waves 42. The

waves in sources 41 and 42 have the same frequency but differ in phase by 90 so that in a manner well understood, a rotating field is produced by the coils 37 and 38.

The windings of coils 30and 40 are. connected in series to the terminalsg33 by means of a switch 43, when in the position shown.

When switch 43 engages the contacts 44, the

coil 31 which is wound and connected to produce a field which opposes that of coil 30 is included in'series withthe windings of coils 30 and 40. v I s vSignal waves are transmitted by transformer 10 to windings 22 0f magnet 23; and

the diaphragm 24 is caused to vibrate in ac-- detector or the like, or to a radio transmitcordance with the amplitude of the received Waves. The movements of the diaphragm 24 are transmitted through the lever arrangement to cause the coils 30 and 31 to be vibrated in opposite directions.

When waves are supplied from sources 41 and 42 to the field coils 37 and 38, and when coils 30 and 31 are stationary, there are induced in coils 30 and 31 carrier waves corresponding to the frequency of the waves from sources 41 and 42. During the vibration of coils 30 and 31 the phase of the induced carrier Waves is modulated or varied in a manner more fully explained in a succeeding part of this description. A modulated wave comprising sideband frequency components and an unmodulated component of carrier frequency, somewhat similar to the corresponding waves produced by ordi-. nary amplitude modulation is produced.

In the stationary coil 40 an unmodulated carrier wave is generatedbutsince this coil is at a position 90 from the mean position of the coils 30 and 31, the phase of the carrier Wave generated therein diifers by 90 from the phase of the unmodulated carrier frequency component of the resulting modulated waves produced in coils 30 and 31.

' With switch 43 in the position shown, the modulated wavesgenerated in coil 30 and the unmodulated carrier waves generated panying unmodulated carrier component from coil 40 after they have been transmitted from a radio transmitting system. The manner in which these waves may be detected will be more fully explained later.

If the switch 43 be thrown to contacts 44, there will be added to the waves from coils 30 and 40, the modulated waves from coil 31. Due to the manner in which coils 31 and 30 are wound these modulated waves will include an unmodulated carrier 'frequency component differing in phase by 180 from the corresponding component of waves from coil 30. Accordingly the unmodulated component of carrier frequency is neutralized and there appear at the terminals 33 only the waves of sideband frequencies accompanied by an unmodulated carrier component from the coil 40 which is 90 differcomponents generated in coils 30 and 31.

These waves may also be combined to efl'ect detection in a manner to be hereinafter described. p a

If desired the coil 40 may be omitted and a suitable source'of carrier waves may be supplied at the rece" ing station to Cause detection of the ph modulatedsidebands. Again the waves-f m'coil 40 may'also be separately transmitted to the receiving station if desired.

In the arrangement shown in the drawings the frequency of waves from the carrier sources 41 and 42 may be arbitrarlly represented by the waves generated in coil may be represented by the express1on:

A cos (pt 0) where- 0 represents the phase angle of the wave induced in the coil 30 as determined by its angular position with respect to the coils 37 and 38, t re resents time and A a constant. When t e coil 30 is vibrated, the base angle varies as a function of this viration and if the vibration is sinusoidal, 0 may be represented by the expression a cos gt for coil 30, for example, and by -a cos gt for coil 31 where the frequency of vibration is represented by and a is a factor, expressed in radians, representing the magnitude of the phase angle variations of coil 30 as determined by the angular vibration of the coil. Thus, the Wave produced in coil 30 during vibration, that is, the phase modulated. wave, may be properly represented by an expression:

M=A cos (pt+a cos gt) (1) The character of this wave will be better understood by analyzing it into its component frequencies. By a trigonometric transformation, the expression may be written:

M=A[cos pt cos (a cos gt) sin pt sin (a, cos qt)] (2) The right-hand cos and sin function, respectively, of each term of equat10n (2) may be and expanded as follows:

a a a i sln (a cos gt) =a cos qtcos qt+ cos tcos gt (4) By substituting the expressions (3) and (4) in equation (2) we have The terms in powers of a are negligible, when a, which represents the amplitude of vibration of coil 30, expressed in radians, is small as compared to unity. After drop- M=A cos zitsin (1)- I=A sin pt-l-B sin pt cos gt+ (8) Upon comparing this expression (8) with equation (6), it will be seen that the unmodulated carrler component in equation (6) is ping all terms above the first power We have M A[cos pt-a sin pt cos gt (6) By a well known trigonometric transformation this equation becomes:

represented by a cos function, whereas in equation (8) it is represented by a sin function. The expressions for the sidebands on the other hand are represented similar functions in the two equations. The physical significance of this difference is that the unmodulated carrier component, in the case of phase modulated waves represented by equation (6) is different in phase with 1 respect to the sideband components than the corresponding unmodulated carrier compo.- nent of am litude modulated waves.

If the "o tage wave represented by equation (7) be supplied to a device operating tector having current relations given by the upon the square law principle, that is, a de The resulting terms that may yield the signal frequency are the product terms in the squared expression and not the square terms, that is, we have the equation:

' z I =ao+a V+ 11 A (cos ptgsin (pi-g) tgsin (p-q) t) (10) After expanding this expression we obterms may be excluded, since the waves reptain terms including second power terms resented thereby are readily separable from representing double the carrier frequency the waves of carrier and sideband frequency. and double the sideband frequencies, which Considering the remaining terms; i. e.

a A(-a cos pt sin (p-tg) t-a cos pt sin (p-q) t) (11) this expression, by trigonometric transforto this particular embodiment, since numermation yields terms representing signalous modifications thereof may be made by a frequency components as follows: person skilled in the art without departing a a from the spirit of applicants invention, the a A( sin gt+ 5 sin gt) (12) scope of which is to be determined by the ap- Since the two terms in this expression are pended claimsj What is claimed is:

equal to each other and opposite in sign, they 1. The method of modulation which comcancel and hence no signal frequencies are prises generating a high frequency carrier produced by the detection process. wave, shifting the phase of said wave to pro- However, if the unmodulated carri r freduce sideband frequencies and an unmoduquency component represented by the term lated carrier frequency component, generatcos pt of equation (6), should have a phase mg a second wave of carrier frequency, 90 different, that is, if it should be represhifting the phase of said second wave so as sented by sin pt, then the signal frequency to generate sidebands 1n phase with said first components resulting fro d t ction would mentloned sldebands and an unmodulated have thesame sign and would not cancel r er frequency component opposite in but would add and a ordingly ignal waves phase to said first mentioned component, and would be derived from the detection of the combining said waves to cause suppression phase modulated waves. Th fun tion f of said first mentioned unmodulated compocoil 40 is to supply an unmodulated carrier nentfrequency wave of the phase necessary for The method of modulation which comthis purpose as alr ady xplain d, prises generating a carrier frequency wave,

By a similar development of equation (1) genemtlng W f h Same fr with the Sig of th t r cos t h d quency but differing 1n phase, causing said it may be readil ho n that in oil 31 a waves to produce a rotating magnetic field, modulated wave is produced in which the g r t ng a earner frequency wave in acsideband components are in phase with the r ence Wl h the rotatlon of said field, and sidebands'of coil 30 but in which the unmods tmg th phase of sand last mentioned ulated carrier frequency component is op- W ve In accordance Wlth signals. posite in phase to the corresponding compo- The method f ion Whl h 0 mnent waves in coil Q0. pr1ses generating a carrier frequency wave,

The invention herein fnaybe used to adg ng a d )Wave of the same "antage for secret signaling, since the modufreq y but d r g 1 Phase by 90 fYOm latedcornponents produced in either coil 30 1,1 first mentloned wave, producing a roor 31 may be transmitted with the unmodut lt gmagnetic' field by the cooperation of lated carrier frequency component, in such d W ves, generatmg aplurahty of carphase relation thereto that detection in unaurier frequency components in accordance thorized receiving circuits would result in with the rotation of said field, shifting the neutralization of the modulating currents, as ase of certain of said components wherecxplained above. However, by supplying y the resultant unmodulated components locally at an'authorized receiving station a produced differ in phase from each other. carrier frequency wave in the proper phase 4. The method of signaling which comrelation to the modulated components, they prises generatlng a rotating magnetic field, may be detected to yield the signals. causing said field to produce a modulated Although this invention has been decomponent and a plurality of components of scribed in connection with a specific embodicarrier frequency, each carrier frequency ment, it is not to be understood as limited component differing in phase from the frequency, and varying the phase of said current in accordance with signals, whereby a wave representedv by the equation:

M:A(cos pta sin pt cos t) is generated.

6. In a modulating system, a source of modulating waves, a source of carrier waves, a second source of carrier waves difiering in phase by 90 from said first carrier waves, means supplied with said carrier waves for producing a rotating magnetic field, means linked by said field and having induced therein a wave of carrier frequency in accordance with the rotation of said field, and means independent of said field for varying the linkage with said means in accordance with signals to cause corresponding variations in the phase of said induced current. 7

7. A modulation system which comprises, a source of signal waves, a source of polyphase carrier waves, means supplied with said carrier waves for generating a rotating magnetic field, vibratory means linked by said magnetic field, so as to have induced therein a carrier frequency current; the vibration of said means being controlled in accordance with signals, whereby corresponding variations in the linkage are produced to cause variations of phase of the induced current.

8. A modulation system which comprises, a source of signal waves, a source of polyphase carrier waves, means supplied with said carrier waves for generating a rotating magnetic field, a plurality of vibratory clements linked by said magnetic field one of said elements being adapted to vibrate in an opposite sense to that of another of said elements, whereby an unmodulated component of carrier frequency induced in said elements is suppressed.

9. The modulation system which comprises a source of signal waves, a source of polyphase carrier waves, means supplied with said carrier waves for generating a rotating magnetic field, a plurality of vibratory coils linked with said field, whereby carrier frequency waves are induced therein, and a stationary coil linked by said field and so arranged that the carrier wave induced therein is different in phase from the waves in said vibratory coils, means for vibrating said coils in accordance with signals, and means for combining the resulting waves from at least one of said vibratory coils, with waves from said stationary coil.

In witness whereof, I hereunto subscribed my name'this 6th day of July, A. D., 1925.

RALPH V. L. HARTLEY. 

